The present invention relates to a separation device comprising a selectively permeable separation medium bonded to a microstructured film that is used in connection with a source for driving a fluid mixture through the device.
Fluid separation devices remove a constituent from a fluid mixture by passing the fluid mixture through a selectively permeable separation medium. The undesirable component(s) of the fluid mixture remain on one side of the separation medium, and the filtrate passes through to the other side of the separation medium. Types of separations available with such devices include gas-solid, gas-gas, gas-liquid, liquid-liquid, and liquid-solid. Applications using these types of separations include water desalinization, dialysis, microfiltration to remove bacteria and other fine particles, detoxification of industrial waste, sewage treatment, and ultrafiltration to remove very fine or dissolved solids from liquids or gases. Typically, these fluid separation devices are at least partially submersed or flooded within the fluid mixture during the separation process.
Transport and control of a fluid mixture through a selectively permeable separation medium may be achieved in a separation system by a fluid transport mechanism independent of the separation medium. An example of this type of system includes a pumping system wherein the fluid mixture is pumped from one tank through a separation medium into another tank. On the other hand, transport and control of the fluid mixture may be achieved as part of a separation device, wherein a separation medium is coupled to a fluid transport mechanism. For example, the separation device may include a vacuum distribution mechanism coupled to a separation medium for driving the fluid mixture through the separation medium by a vacuum source.
The transport of fluid by a conduit or other device may be characterized based on the mechanism that causes flow within the conduit or device. Where fluid transport pertains to a nonspontaneous fluid flow regime wherein the fluid flow results, for the most part, from an external force applied to the device, such fluid transport mechanism is considered active. On the other hand, where the fluid transport pertains to a spontaneous flow regime wherein the fluid movement stems from a property inherent to the transport device, such fluid transport mechanism is considered passive. A catheter is a well-known example of an active fluid transport device. Typically, catheters that are used in the medical field to drain fluid from a body cavity are connected to a vacuum source to draw the liquid through the device. A passive fluid transport device is an absorbent pad.
Active fluid transport products have been developed based upon specific applications, including absorbent pads or a liquid pervious layer combined with fluid transport devices. For example, mat products including active fluid transport and absorbent pads or liquid pervious layers are described in U.S. Pat. No. 5,437,651 to Todd et al., and U.S. Pat. No. 5,349,965 to McCarver. In each case, channels are defined on a surface of a substrate to direct liquid flow from substantially all of the area of a liquid pervious layer. These products remove liquid while having the liquid pervious layer act as a liquid absorbing and storing layer and/or to define a liquid receiving chamber. In Todd et al., a flexible backing plate is attached to an absorbent portion, and a suction source is applied to the backing plate. The backing plate comprises a plurality of channels for directing the vacuum provided by the suction source more evenly across the surface of the absorbent portion. In McCarver, a flexible pad or suction rail having a liquid permeable top surface and a liquid impermeable bottom surface is connected to a vacuum source. The suction draws liquid down into a liquid receiving chamber as it passes through the liquid pervious layer, and draws the accumulated liquid away. The liquid receiving chamber contains separation means dividing the chamber into channels for keeping the chamber from collapsing when the chamber is placed under a negative pressure.
Another flexible fluid transport product has been recently introduced and is commercially available under the tradename xe2x80x9cFluid Controlxe2x80x9d floor suction mat, from Technol Medical Products Inc. This product is used to absorb fluids that fall from a surgical site during a surgical procedure. The device has an absorbent mat that resides above a multitude of parallel enclosed channels. Holes are provided in the channel surfaces that interface with the absorbent mat so that fluid recovered by the mat can be drawn into the channels. The parallel channels are connected to a manifold for attachment with suction tubing. Thus, after fluid has accumulated within the mat, removal thereof can be facilitated through the multiple channels by the application of vacuum.
Examples of flexible fluid transport devices that utilize both active and passive fluid transport are described in U.S. Pat. No. 3,520,300 to Flower, U.S. Pat. No. 4,747,166 to Kuntz, and U.S. Pat. No. 5,628,735 to Skow. In Flower, a surgical sponge and suction device is disclosed having an absorbent material over a perforated wall of a chamber that is connected to a vacuum source via a tube. In Kuntz, a pad, having an absorbent core encased in hydrophobic material but with a perforated top surface, surrounds a perforated tube coupled to a vacuum source. In Skow, a mat is provided comprising a material having a high wicking property, and within the material, a flexible suction tube is provided for preventing the mat from becoming saturated with fluid. In all three cases, the tubing limits where the fluid is evacuated from within the device.
Examples of other channeled mats for fluid removal are shown in U.S. Pat. No. 4,533,352 to Van Beek et al. and U.S. Pat. No. 4,679,590 to Hergenroeder; however, these mats provide structure for receiving fluid without defining a receiving chamber closed by a liquid pervious layer. Van Beek et al. shows a ribbed mat with a centrally located suction hose connected to the ribs by openings in the hose. Hergenroeder shows a mat having a gridwork of small basins forming a collection surface that are drained into channels connected to a suction source.
Examples of passive fluid transport devices having channeled fluid transport structures are described in PCT International Publication No. WO 93/11727, entitled xe2x80x9cLiquid Management Member For Absorbent Articles.xe2x80x9d Disclosed is the use of a liquid management member having a microstructure-bearing hydrophilic surface, preferably in combination with a liquid permeable top sheet, a back sheet, and an absorbent core disposed between the top and back sheets. The liquid management member promotes rapid directional spreading of liquids and is in contact with the absorbent core.
Specific examples of fluid separation devices include the type disclosed in U.S. Pat. No. 5,455,771 to Degen. In the Degen patent, a collection of fine, hollow, permeable or semi-permeable fiber strands are used as a fluid transport device. These hollow fibers may filter a fluid by passing it over the exterior of the fibers and/or by passing the fluid through the fiber walls and into the interior of the fibers. Problems associated with these types of separation devices include problems with the production of the fibers. Moreover, hollow fiber separation devices are limited in application and susceptible to a number of problems. Fiber fragility and the general difficulty of handling bundles of small individual elements hampers their use. High unit cost, fouling, and a lack of geometric (profile) flexibility further limit application of these fibers as a fluid transport mechanism in separation devices. The inability to practically distribute long lengths and large numbers of hollow fibers into useful transport arrays makes their use inappropriate for all but a limited range of active fluid transport applications.
The present invention overcomes the disadvantages and shortcomings of the prior art by providing a separation device that is flexible, efficient, easy to handle and use, inexpensive to manufacture, and extremely versatile and adaptable to various separation applications. More specifically, the present invention provides a separation device comprising a separation module formed from a structured layer having a plurality of flow channels and a separation media, as well as a source providing a potential across the flow channels of the structured layer to drive a fluid mixture through the separation media in order to remove a constituent(s) from the fluid mixture.
The separation module preferably includes a manifold connected in fluid contact with the flow channels of the structured surface. The manifold may be connected to the source, or may be connected to a receptacle or to another device. The source provided as part of the separation device may connect to the manifold, or may connect to the separation module in some other manner. The source may be a vacuum that pulls a fluid mixture through the separation media, into the flow channels and out through the manifold, or it may pull a fluid mixture through the manifold, into the flow channels and across the separation media. Alternatively, the source may be a pressure source, such as a pump, that pushes the fluid mixture through the separation media in either direction discussed above.
The separation media comprises selectively permeable separation material, such as microporous film, micro-perforated film, nonwoven filtration web, or other types of filtration material. The separation module may be formed with a single layer of separation media, or it may have multiple layers that are all the same, or are different from one another, depending on the separation application.
The flow channels of the structured layer are defined by a series of peaks whose sidewalls may converge, or that may be separated by a planar floor. Alternatively, the peaks may be separated by at least one sub-peak forming sub-channels within each flow channel. The flow channels may vary across the structured surface, channel to channel, or within each channel. The structured surface may be formed from a polymer such as polytetrafluoroethylene or polypropylene, or other suitable material.
In another embodiment, the separation module may comprise more than one structured layer at least partially covered by a separation media. A manifold in fluid contact with the flow channels of the first layer would also be in fluid contact with the flow channels of at least one other layer.
The present invention also teaches a method of removing a constituent from a fluid mixture comprising the steps of providing a separation module of the present invention, connecting the module to an externally provided source to form the separation device, flooding the module within a fluid mixture to be filtered, and driving the fluid mixture through the module by the source, thereby removing a constituent(s) from the fluid mixture. This method may also encompass a source that is a vacuum or a source that is a pressure source. The method may drive the fluid mixture through a manifold into the flow channels of the structured layer and across the separation media, or it may drive fluid through the separation media into the flow channels and out through the manifold. The separation module of the method may have a single separation media layer, or it may include multiple separation media layers that are either the same or different from one another.